Our long term goal is to understand the control mechanisms of carbohydrate metabolism in various mammalian tissues and yeast. Specifically, we are interested in the regulation of phosphofructokinase, one of the key enzymes of glycolysis. Currently we are investigating the physiological importance of a covalent modification of phosphofructokinase in liver and heart. We are also studying the roles of fructose-2, 6-P2, a recently discovered potent activator of phosphofructokinase. Synthesis and degradation of fructose-2,6-P2 is catalyzed by a bifunctional enzyme, fructose-6-P,2-kinase and fructose-2,6-bisphosphatase. We plan to purify and characterize heart fructose-6-P, 2- kinase:fructose-2, 6-bisphosphatase. The study of the structure and the function of the liver bifunctional enzyme will be continued. Of particular interest with this bifunctional enzyme is phosphorylation which leads to opposite activities depending on the tissue sources. Using perfused heart and isolated myocytes the physiological significance of phosphorylation will be investigated as well as the effects of various alpha and beta agonists and cardiac work on the bifunctional enzymes and also on phosphofructokinase will be studied.